An ethylene tar-based liquid-phase coated pitch for fast-charging negative electrodes of lithium batteries and its preparation method

Abstract

This invention discloses an ethylene tar-based liquid-phase coated pitch for fast-charging negative electrodes of lithium-ion batteries and its preparation method, relating to the field of new energy materials technology. It solves the technical problems of traditional coated pitches, such as high quinoline insoluble content, poor fluidity, unsatisfactory fast-charging performance, and low added value of ethylene tar. The preparation method uses ethylene tar as raw material, which is finely fractionated through three-stage distillation to obtain aromatic components with specific distillation ranges. These components are then homogenized and blended with heavy reactive components, followed by a catalytic cross-linking reaction under a catalyst and oxygen-containing atmosphere to obtain the ethylene tar-based liquid-phase coated pitch. The coated pitch prepared by this invention is liquid at room temperature, with a quinoline insoluble content ≤0.1%. When applied to the coating of fast-charging negative electrodes of lithium-ion batteries, it exhibits a 2C / 0.5C capacity retention rate ≥93%, an initial efficiency ≥92%, a comprehensive utilization rate of ethylene tar ≥98%, and a product yield ≥56%. The process is continuous, easily industrialized, and conforms to the concept of green and sustainable development.

Description

Technical Field

[0001] This invention relates to the field of new energy materials technology, and more specifically, to an ethylene tar-based liquid-phase coated pitch for fast-charging negative electrodes of lithium batteries and its preparation method. Background Technology

[0002] Lithium-ion batteries are widely used in new energy vehicles, energy storage devices, and other fields due to their high energy density and long cycle life. With the expansion of application scenarios, the market is placing higher demands on the fast-charging performance and cycle stability of lithium batteries. Graphite-based materials are the mainstream anode materials for lithium batteries, and surface coating modification is a key means to improve the electrochemical performance of the battery. Asphalt coating, as a core coating agent, can form an amorphous carbon protective layer on the graphite surface, reducing side reactions between the electrolyte and graphite, and inhibiting the peeling of graphite sheets during charging and discharging, thereby improving the battery's initial coulombic efficiency, reversible capacity, and cycle life.

[0003] Currently, the traditional production process of coating asphalt for lithium battery anodes has many technical defects: First, the content of quinoline insolubles in the product is generally higher than 5%, resulting in poor fluidity of the coating asphalt, poor wetting of graphite, and unevenness and cracking of the coating layer, which seriously affects the fast charging performance of the battery; Second, the production process is mostly intermittent, resulting in large fluctuations in product quality and a product yield of less than 40%, leading to high production costs; Third, the raw materials are mostly dense polycyclic aromatic hydrocarbons, which contain almost no branched free radicals, resulting in poor raw material adaptability and making it difficult to optimize the performance of the coating asphalt through structural control.

[0004] Ethylene tar, a byproduct of ethylene production, contains over 80% aromatic compounds and is extremely low in sulfur, nitrogen, and ash, making it an ideal raw material for preparing coated bitumen. However, it is currently mainly used as a raw material for fuel oil or carbon black production, resulting in low resource added value and a lack of high-value utilization. Existing technologies have attempted to use ethylene tar to prepare coated bitumen, but these are mostly simple mixing and cross-linking methods without fine fractionation of the ethylene tar. This prevents precise control of the molecular structure of the coated bitumen, and the resulting products still suffer from poor flowability and unsatisfactory fast-charging performance, failing to meet the application requirements of fast-charging anodes for lithium batteries. Therefore, developing a liquid-phase coated bitumen based on the fine utilization of ethylene tar, with low quinoline insolubles, high flowability, and significantly improved fast-charging performance of lithium batteries, and its preparation method, has become a key research focus in the field of new energy materials. Summary of the Invention

[0005] In order to overcome the defects in the performance and process of lithium battery coating asphalt in the existing technology, the lack of fine fractionation of ethylene tar-based coating asphalt, low resource utilization and poor product performance, this invention discloses an ethylene tar-based liquid phase coating asphalt for fast-charging negative electrodes of lithium batteries and its preparation method, which can effectively solve the above-mentioned technical problems.

[0006] To solve the above-mentioned technical problems, the technical solution of the present invention is as follows:

[0007] A method for preparing ethylene tar-based liquid-phase coated pitch for fast-charging negative electrodes of lithium batteries includes the following steps:

[0008] Raw material distillation and fractionation: Ethylene tar is finely separated by a three-stage distillation system, and aromatic components are collected in two distillation ranges of 180-220℃ and 240-260℃, while heavy reactive components are also obtained;

[0009] Fraction homogenization and blending: The aromatic components of the two distillation ranges in step 1) are mixed with the heavy reactive components at a mass ratio of 1:(0.5-2), and homogenization reaction is carried out under inert gas protection to obtain liquid-phase coated asphalt precursor;

[0010] Catalytic crosslinking reaction: The liquid-phase coated asphalt precursor is subjected to a catalytic crosslinking reaction under a catalyst and an oxygen-containing atmosphere to obtain the ethylene tar-based liquid-phase coated asphalt.

[0011] Preferably, the distillation process of the three-stage distillation system in step 1) is as follows: after the ethylene tar is preheated, it enters the first distillation column, and the fuel oil fraction is separated at the top of the column; the bottom material of the first column enters the second distillation column, and the light components are separated at the top of the column; part of the bottom material of the second column is sent to the reaction system, and part enters the third distillation column, the high-range fuel oil fraction is separated at the top of the third distillation column, and the heavy reaction components are obtained at the bottom of the column; aromatic components at 180-220℃ and 240-260℃ are collected at the top of the second and / or third distillation columns.

[0012] Preferably, the conditions for the homogenization reaction in step 2) are: reaction temperature 120-160℃, stirring speed 300-800r / min, and reaction time 1-4h; the amount of the reaction weight component added is 5-15% of the total mass of the aromatic components.

[0013] Preferably, the catalyst in step 3) is a metal oxide catalyst and / or a molecular sieve catalyst, and the amount of catalyst added is 0.1-1% of the total mass of the liquid-phase coated asphalt precursor.

[0014] Preferably, the process conditions for the catalytic crosslinking reaction in step 3) are: reaction temperature 300-360℃, reaction pressure 0.5-1.5MPa, reaction time 2-8h; the oxygen-containing atmosphere is air with an oxygen volume fraction of 0-2% and an air flow rate of 1-3L / (min·kg) for liquid-phase coated asphalt precursor.

[0015] Preferably, the ethylene tar in step 1) has an aromatic compound content of ≥80% and a total sulfur, nitrogen and ash content of ≤0.5%.

[0016] Preferably, the inert gas in step 2) is one or a mixture of nitrogen and argon.

[0017] Preferably, an ethylene tar-based liquid-phase coated asphalt for fast-charging negative electrodes of lithium batteries is prepared by the preparation method described above. The coated asphalt is liquid at room temperature, has a quinoline insoluble content of ≤0.1%, and a coking value of 18-28%.

[0018] Preferably, the application of an ethylene tar-based liquid-phase coated pitch in lithium battery anode materials involves coating the coated pitch onto the surface of a graphite-based anode material, followed by carbonization to obtain a fast-charging lithium battery anode material. The carbonization conditions are: carbonization temperature 900-1100℃, carbonization time 1-3h, and carbonization atmosphere is an inert gas atmosphere. The coating amount of the coated pitch is 8-12% of the mass of the graphite-based anode material.

[0019] Preferably, a lithium battery fast-charging negative electrode material includes a graphite substrate and a carbon coating layer on the surface of the substrate, wherein the carbon coating layer is formed by carbonization of the ethylene tar-based liquid phase coated pitch described above; the negative electrode material has a 2C / 0.5C capacity retention rate ≥93%, an initial coulombic efficiency ≥92%, and a capacity retention rate ≥95% after 100 cycles.

[0020] Compared with the prior art, the beneficial effects of the present invention are as follows: The ethylene tar-based liquid-phase coated pitch prepared by the present invention for the fast-charging negative electrode of lithium battery achieves the performance advantages of room temperature liquid state, low quinoline insoluble matter (≤0.1%), and high coking value through fine fractionation and molecular structure control of ethylene tar, solving the problems of poor fluidity and uneven coating of traditional coated pitch; when applied to the graphite negative electrode of lithium battery, the carbon coating layer formed can effectively reduce electrolyte side reactions and inhibit graphite sheet peeling, so that the 2C / 0.5C capacity retention rate of the negative electrode material is ≥93%, the initial coulombic efficiency is ≥92%, and the capacity retention rate after 100 cycles is ≥95%, which significantly improves the fast-charging performance and cycle stability of lithium battery. The preparation process of this invention adopts a continuous three-stage distillation and multi-stage reaction vessel system, with a product yield of ≥56%, which is much higher than the 40% of the traditional process. Moreover, the comprehensive utilization rate of ethylene tar is ≥98%, realizing the high-value utilization of ethylene tar by-products and reducing production costs. At the same time, the process reaction conditions are mild, the operation is simple, and no harmful by-products are generated, which is in line with the development trend of green chemical industry and new energy industry, and has good prospects for industrial application and market value. Attached Figure Description

[0021] To more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are merely exemplary. For those skilled in the art, other embodiments can be derived from the provided drawings without creative effort.

[0022] Figure 1 This diagram illustrates the steps of a method for preparing ethylene tar-based liquid-phase coated pitch for use as a fast-charging negative electrode in lithium batteries. Detailed Implementation

[0023] The accompanying drawings are for illustrative purposes only and should not be construed as limiting the scope of this patent.

[0024] To better illustrate this embodiment, some parts in the accompanying drawings may be omitted, enlarged, or reduced, and do not represent the actual product dimensions;

[0025] It will be understood by those skilled in the art that certain well-known structures and their descriptions may be omitted in the accompanying drawings.

[0026] The embodiments of this application will be further described in detail below with reference to the accompanying drawings and examples.

[0027] It is understood that the specific embodiments described herein are merely illustrative of the embodiments of this application and are not intended to limit the embodiments of this application. Furthermore, it should be noted that, for ease of description, the accompanying drawings only show the parts related to the embodiments of this application, not all structures. Those skilled in the art, after reading this specification, should be able to realize that any combination of technical features can constitute an optional implementation method, provided that the technical features do not contradict each other.

[0028] The terms "first," "second," etc., used in the specification and claims of this application are used to distinguish similar objects and not to describe a specific order or sequence. It should be understood that such use of data can be interchanged where appropriate so that embodiments of this application can be implemented in orders other than those illustrated or described herein, and the objects distinguished by "first," "second," etc., are generally of the same class and the number of objects is not limited; for example, a first object can be one or more. Furthermore, in the specification and claims, "and / or" indicates at least one of the connected objects, and the character " / " generally indicates that the preceding and following objects are in an "or" relationship. In the description of this application, "multiple" means two or more, and "several" means one or more.

[0029] This invention discloses an ethylene tar-based liquid-phase coated pitch for fast-charging negative electrodes of lithium-ion batteries and its preparation method. Using high-aromatic-content ethylene tar as the core raw material, a continuous process involving three-stage distillation to finely separate aromatic components within specific distillation ranges, homogenization and blending of the fractions, and catalytic cross-linking reactions, is employed to obtain a high-performance liquid-phase coated pitch with low quinoline insoluble content at room temperature. When applied to graphite negative electrodes of lithium-ion batteries, this product significantly improves the fast-charging performance and cycle stability of the battery. The following detailed disclosure of this invention is provided in conjunction with multiple embodiments, comparative examples, and application test cases. All embodiments are for illustrative purposes only and are not intended to limit the scope of protection of this invention. Those skilled in the art can implement all the technical solutions of this invention based on these embodiments without any creative effort.

[0030] The ethylene tar used in this embodiment meets the technical requirements of aromatic compound content ≥80% and total sulfur, nitrogen and ash content ≤0.5%, and is a by-product generated during the ethylene industrial cracking process; the catalysts used are industrial-grade metal oxide catalysts (alumina, zinc oxide) and molecular sieve catalysts (ZSM-5 type), both of which are conventional catalytic materials in the chemical industry; the inert gases are industrial-grade nitrogen and argon, with a purity ≥99.99%; the graphite anode material is the artificial graphite (particle size 15-20μm) and natural graphite (particle size 10-15μm) commonly used in lithium battery anodes, without any special modification treatment.

[0031] Example 1

[0032] Optimal process parameters for preparing ethylene tar-based liquid-phase coated pitch.

[0033] Please see Figure 1Step 1: Raw Material Distillation and Fractionation. A three-stage atmospheric distillation system consisting of a first distillation column, a second distillation column, and a third distillation column is used for the fine separation of ethylene tar. All columns are filled with stainless steel θ-ring packing to improve fraction separation efficiency. First, the ethylene tar is heated to 120°C via a preheater and continuously fed into the first distillation column. The top temperature of the first distillation column is controlled at 150-180°C, and a light fuel oil fraction is separated at the top, which is collected after condensation as an industrial by-product for recycling. The heavy material at the bottom of the first distillation column flows continuously into the second distillation column by gravity. The top temperature of the second distillation column is controlled at 200-230°C, and a lighter component is further separated at the top, which is also collected as a fuel oil component after condensation. The material at the bottom of the second distillation column is divided into two streams at a 1:1 flow ratio. One stream flows directly into the second distillation column. One stream is sent to the reaction system for standby, while another stream is continuously fed into a three-column distillation system. By precisely controlling the top temperature of the three-column distillation system, the fractions are cut sequentially into two distillation ranges: 180-220℃ and 240-260℃. Aromatic components from 180-220℃ and 240-260℃ are collected respectively, with yields of 15.2% and 18.7% for the two fractions. When the top temperature of the three-column distillation system exceeds the above two ranges, a high-range fuel oil fraction is separated from the top of the column, and a brownish-black viscous reaction heavy component is collected from the bottom of the column and sealed for later use.

[0034] Step 2: Fraction Homogenization and Preparation. Weigh the 180-220℃ aromatic component and the 240-260℃ aromatic component prepared above at a mass ratio of 1:1.2. Add both fractions to a liquid-phase coating agent tank equipped with a frequency converter, an inert gas inlet device, and a temperature control system. Then add 10% of the total mass of the two aromatic components as a reaction weight component, and mix to obtain a homogenized base material. Continuously purge nitrogen into the liquid-phase coating agent tank, and after purging the air inside, maintain a slight positive pressure protection state with the nitrogen pressure controlled at 0.02 MPa. Turn on the converter and adjust the stirring speed to 500 r / min. Simultaneously heat the liquid-phase coating agent tank, controlling the material temperature inside the tank at 140℃. Under these process conditions, maintain a constant temperature homogenization reaction for 2 hours. During the reaction, keep the stirring and nitrogen protection uninterrupted. Finally, obtain a homogeneous, transparent, light yellow liquid-phase coated asphalt precursor. This precursor exhibits no stratification, no sedimentation, and good fluidity.

[0035] Step 3: Catalytic Crosslinking Reaction. The prepared liquid-phase coated asphalt precursor is continuously fed into a two-stage series high-pressure reactor using a gear pump. 0.3% (by mass) of ZSM-5 molecular sieve catalyst is added to the reactor. The catalyst is fed in a slurry and thoroughly mixed with the precursor to ensure uniform catalytic reaction. The reactor process parameters are adjusted: reaction temperature is controlled at 340℃, reaction pressure at 0.8MPa, and reaction time at 4h. During the reaction, an oxygen-containing atmosphere (2% oxygen by volume) is continuously introduced into the reactor at a flow rate precisely controlled at 2L / (min·kg) of liquid-phase coated asphalt precursor. This oxygen-containing atmosphere promotes appropriate crosslinking between material molecules, preventing excessive condensation that could degrade product performance. After the catalytic crosslinking reaction is complete, the material in the reactor is cooled to 80℃ and filtered through a precision filter to remove any remaining catalyst residue, yielding the final ethylene tar-based liquid-phase coated asphalt product.

[0036] The performance of the ethylene tar-based liquid-phase coated pitch prepared in this embodiment was tested. The results showed that the product was a light yellow liquid at room temperature and pressure, with excellent fluidity and no obvious viscous clumping. The quinoline insoluble content was 0.05%, and the coking value was 19%. The comprehensive utilization rate of ethylene tar in this embodiment reached 98.5%, and the product yield was 58%, both of which were better than the existing technical indicators.

[0037] Example 2

[0038] Ethylene tar-based liquid-phase coated pitch was prepared by using a high proportion of tricyclic aromatic hydrocarbon fractions and a metal oxide catalyst.

[0039] Please see Figure 1 Step 1: Raw material distillation and fractionation. The raw material distillation and fractionation steps in this embodiment are completely consistent with those in Example 1. The same three-stage distillation system, process parameters, and operating methods are used to finely separate the same batch of ethylene tar, collecting aromatic components at 180-220℃, aromatic components at 240-260℃, and reactive heavy components. The yields of each fraction are consistent with those in Example 1.

[0040] Step 2: Fraction Homogenization and Preparation. Weigh the aromatic components at a mass ratio of 1:0.8 (180-220℃ and 240-260℃), add them to the liquid phase coating agent tank, and then add 8% (by mass) of the total mass of the two aromatic components as a reaction weight component. Mix to obtain the base material. Continuously purge the liquid phase coating agent tank with argon gas, and after purging the air, maintain a slight positive pressure of 0.02 MPa. Turn on the stirrer and adjust the stirring speed to 600 r / min. Heat the material to 160℃ and homogenize under these conditions for 1.5 hours to obtain a homogeneous, pale yellow liquid phase coated asphalt precursor.

[0041] Step 3: Catalytic cross-linking reaction. The liquid-phase coated asphalt precursor was fed into a two-stage series high-pressure reactor. 0.5% (by mass) of alumina metal oxide catalyst was added, and after thorough mixing, the reactor parameters were adjusted as follows: reaction temperature 360℃, reaction pressure 1.0 MPa, and reaction time 3 h. During the reaction, air with an oxygen volume fraction of 1.5% was introduced at a flow rate of 1.5 L / (min·kg) of precursor to promote molecular cross-linking. After the reaction was completed, the product was cooled and filtered to obtain the ethylene tar-based liquid-phase coated asphalt product.

[0042] The product prepared in this embodiment is liquid at room temperature, with a quinoline insoluble content of 0.07% and a coking value of 26%; the comprehensive utilization rate of ethylene tar is 98.2%, and the product yield is 56.5%. All performance indicators meet the technical requirements of this invention.

[0043] Example 3

[0044] Ethylene tar-based liquid-phase coated pitch was prepared by adjusting the lower limit ratio of distillate and using composite catalysts.

[0045] Please see Figure 1 Step 1: Raw material distillation and fractionation. The three-stage distillation process, equipment, and operating conditions in this embodiment are exactly the same as in Example 1, which finely separates ethylene tar and collects the target aromatic components and reactive heavy components.

[0046] Step 2: Fraction Homogenization and Blending. Weigh the aromatic components at 180-220℃ and 240-260℃ according to the lower limit ratio of 1:0.5 specified in this invention. Add them to the liquid-phase coating agent tank, then add 5% of the total mass of the two aromatic components as a reaction weight component, and mix to obtain the base material. Maintain a slight positive pressure by purging with nitrogen, adjust the stirring speed to 300 r / min, heat the material to 130℃, and homogenize at this constant temperature for 3 hours to obtain the liquid-phase coated asphalt precursor.

[0047] Step 3: Catalytic cross-linking reaction. Add 0.1% (by weight of the total mass of the liquid-coated asphalt precursor) of zinc oxide metal oxide catalyst to the reactor. This addition amount is the lower limit of the permitted catalyst addition amount. Adjust the reactor parameters as follows: reaction temperature 320℃, reaction pressure 1.2 MPa, reaction time 6 h. During the reaction, introduce air with an oxygen volume fraction of 1% at a flow rate of 2.5 L / (min·kg) of the precursor. After the reaction is complete, cool and filter to obtain the finished product.

[0048] The product prepared in this embodiment is liquid at room temperature, with a quinoline insoluble content of 0.08% and a coking value of 20%. The comprehensive utilization rate of ethylene tar is 98.3%, and the product yield is 56.2%. Even with the fraction blending and catalyst addition at the lower limit, it still maintains excellent product performance.

[0049] Example 4

[0050] Ethylene tar-based liquid-phase coated pitch was prepared by adjusting the upper limit ratio of distillate blending and the upper limit of catalyst addition.

[0051] Please see Figure 1 Step 1: Raw material distillation and fractionation. Ethylene tar was separated using the same three-stage distillation process as in Example 1, collecting aromatic components and heavy reactive components at 180-220℃ and 240-260℃.

[0052] Step 2: Fraction Homogenization and Blending. Weigh two aromatic components according to the upper limit ratio of 1:2 specified in this invention, add them to the liquid phase coating agent tank, and then add 12% of the total mass of the two aromatic components as a reaction weight component. Mix to obtain the base material. Probe with nitrogen under slight positive pressure protection, adjust the stirring speed to 700 r / min, heat the material to 150℃, and homogenize at this constant temperature for 2.5 h to obtain the liquid phase coated asphalt precursor.

[0053] Step 3: Catalytic cross-linking reaction. Add 1.0% (by weight of the total mass of the liquid-coated asphalt precursor) of ZSM-5 molecular sieve catalyst to the reactor, which is the upper limit of the catalyst addition amount. Adjust the reactor parameters as follows: reaction temperature 350℃, reaction pressure 1.5MPa (the upper limit of pressure specified in this invention), and reaction time 2h (the lower limit of time specified in this invention). During the reaction, pure air (0% oxygen by volume) is introduced at a flow rate of 3L / (min·kg) of precursor. After the reaction is complete, cool and filter to obtain the finished product.

[0054] The product prepared in this embodiment is liquid at room temperature, with a quinoline insoluble content of 0.09% and a coking value of 25%. The comprehensive utilization rate of ethylene tar is 98.1%, and the product yield is 56.8%. Even under process conditions where the fraction blending, reaction pressure, catalyst addition amount are at the upper limit, and reaction time is at the lower limit, the product still meets the core performance requirements of this invention.

[0055] Example 5

[0056] Ethylene tar-based liquid-phase coated pitch was prepared by nitrogen-argon mixed gas protection and long-term homogenization reaction.

[0057] Please see Figure 1 Step 1 involves the fractional distillation of the raw materials. This process is identical to that in Example 1, separating ethylene tar to obtain the target fraction and the heavy reactive components.

[0058] Step 2: Fraction Homogenization and Blending. Weigh two aromatic components at a mass ratio of 1:1.5, add them to the liquid phase coating agent tank, and then add 15% of the total mass of the two aromatic components as a reaction weight component. Mix to obtain the base material. Pour a nitrogen-argon mixture (nitrogen:argon = 1:1) into the tank, maintaining a slight positive pressure. Adjust the stirring speed to 800 r / min, heat the material to 120℃, and homogenize at this constant temperature for 4 hours to complete the homogenization and blending of the material, obtaining the liquid phase coated asphalt precursor.

[0059] Step 3: Catalytic cross-linking reaction. Add 0.8% (by weight of the total mass of the liquid-coated asphalt precursor) of a zinc oxide-molecular sieve composite catalyst (zinc oxide:ZSM-5 molecular sieve = 1:1) to the reactor. Adjust the reactor parameters as follows: reaction temperature 310℃, reaction pressure 0.6MPa, reaction time 7h. During the reaction, introduce air with an oxygen volume fraction of 0.5% at a flow rate of 1.2L / (min·kg) of the precursor. After the reaction is complete, cool and filter to obtain the final product.

[0060] The product prepared in this embodiment is liquid at room temperature, with a quinoline insoluble content of 0.06% and a coking value of 23%. The comprehensive utilization rate of ethylene tar is 98.4%, and the product yield is 57.5%. Mixed gas protection and long-term homogenization reaction further improve the uniformity and performance stability of the product.

[0061] Comparative Example 1: Preparation of Lithium-ion Battery Anode Coated Asphalt Using a Traditional Intermittent Process. This comparative example uses a traditional intermittent thermal polymerization process to prepare coated asphalt. Dense pure polycyclic aromatic hydrocarbons are used as raw materials, with 5% (by mass) of a traditional crosslinking agent added. The materials are added to an intermittent reactor and subjected to thermal polymerization at 380℃ and 2.0 MPa for 6 hours. After the reaction, the mixture is allowed to cool naturally to room temperature to obtain the traditional coated asphalt product. Performance testing of this product shows that it is solid at room temperature and requires heating to above 180℃ to melt, exhibiting extremely poor fluidity. The quinoline insoluble content is 6.2%, significantly higher than that of the product of this invention. The coking value is 15%, the product yield is only 38%, and the raw material utilization rate is 75%. All indicators are significantly inferior to those of the product of this invention.

[0062] Comparative Example 2: Direct crosslinking of ethylene tar to prepare coated asphalt (without fine fractionation). This comparative example directly used raw ethylene tar without undergoing three-stage distillation as raw material. No fractionation or blending was performed; the ethylene tar was directly fed into the reactor, and 0.5% (by mass) of ZSM-5 molecular sieve catalyst was added. The reaction was carried out for 4 hours at 340℃ and 0.8 MPa, the same conditions as in Example 1, with 2% oxygen-containing air introduced. After the reaction was completed, the coated asphalt product was obtained by cooling. Performance testing results showed that the product was semi-solid at room temperature, with poor fluidity and obvious stratification; the quinoline insoluble content was 2.8%, and the coking value was 17%; the comprehensive utilization rate of ethylene tar was only 80%, and the product yield was 45%. Due to the lack of fine fractionation, precise control of the molecular structure could not be achieved, and the product performance fell far short of the application requirements for fast-charging negative electrodes in lithium batteries.

[0063] Application Test Example: Application and Performance Verification of Ethylene Tar-Based Liquid-Phase Coated Pitch in Lithium-ion Battery Anodes.

[0064] The coated asphalt products prepared in Examples 1-5 and Comparative Examples 1-2 were applied to the coating modification of graphite anodes for lithium batteries. Uncoated raw graphite substrates were used as a blank control group for electrochemical performance comparison tests. The coating modification process for all samples was kept consistent, and the specific operation was as follows: The coated asphalt was mixed with graphite anode material at a mass ratio, and anhydrous ethanol was added as a dispersant. The mixture was stirred in a high-speed mixer at a speed of 1000 r / min for 30 min to ensure uniform adsorption of the coated asphalt onto the surface of the graphite particles. The mixed material was placed in a tube furnace and heated to the carbonization temperature at a heating rate of 5℃ / min under an inert gas protective atmosphere, and carbonized at a constant temperature for a specified time. After carbonization, the material was naturally cooled to room temperature, ground, and sieved to obtain lithium battery anode material. Subsequently, coin cells were prepared for electrochemical performance testing.

[0065] In this application test case, the core test group was the optimal process product prepared in Example 1. The effects of different coating amounts (8%, 10%, and 12%, which are the coating amount ranges defined in this invention) and different graphite substrates (artificial graphite and natural graphite) on electrochemical performance were investigated. Simultaneously, the product of Example 1 was compared with the products of Comparative Examples 1 and 2 and the blank control group to verify the performance advantages of the product of this invention. The coating amount was defined as the percentage of the mass of the coated asphalt to the total mass of the graphite-based anode material. The carbonization temperature was uniformly set at 1000℃, the carbonization time was uniformly set at 2 hours, and the carbonization atmosphere was nitrogen protection.

[0066] Test results show that the product in Example 1, with a coating amount of 10% and an artificial graphite substrate, achieved optimal electrochemical performance, with an initial coulombic efficiency of 92.3%, a reversible capacity of 355 mAh / g, a 2C / 0.5C capacity retention rate of 93.8%, and a capacity retention rate of 95.2% after 100 cycles. When the coating amount was adjusted within the range of 8%-12%, all electrochemical performance indicators remained at a high level. With a coating amount of 8%, the initial coulombic efficiency slightly increased to 92.5%, the reversible capacity was 353 mAh / g, and the 2C / 0.5C capacity retention rate was 93.5%. With a coating amount of 12%, the initial coulombic efficiency was 92.0%, the reversible capacity was 354 mAh / g, and the 2C / 0.5C capacity retention rate was 93.6%, all meeting the performance requirements of lithium battery fast-charging anodes.

[0067] When the product of Example 1 is applied to a natural graphite substrate, under the condition of 10% coating, the initial coulombic efficiency is 91.5%, the reversible capacity is 346 mAh / g, the 2C / 0.5C capacity retention rate is 92.9%, and the capacity retention rate after 100 cycles is 94.7%. Although it is slightly lower than that of artificial graphite substrate, the performance improvement effect is significant compared with uncoated natural graphite, proving that the product of the present invention has good coating adaptability to different graphite substrates.

[0068] The products prepared in Examples 2-5, when applied to artificial graphite substrates with a coating amount of 10%, maintained high levels of various electrochemical performance indicators. The initial coulombic efficiency was ≥91.7%, the reversible capacity was ≥348mAh / g, the 2C / 0.5C capacity retention rate was ≥91.5%, and the capacity retention rate after 100 cycles was ≥93.6%, all of which met the performance requirements of lithium battery fast-charging anode materials as defined in this invention. Comparative test results show that the uncoated graphite substrate has the worst electrochemical performance, with a 2C / 0.5C capacity retention rate of only 82.1% and a capacity retention rate of 85.2% after 100 cycles. Although the traditional process product of Comparative Example 1 shows some improvement, the 2C / 0.5C capacity retention rate is only 85.3% and the capacity retention rate after 100 cycles is 89.7%, which cannot meet the fast charging requirements. The product prepared from unfractionated ethylene tar in Comparative Example 2 has better performance than the traditional product, but the 2C / 0.5C capacity retention rate is only 88.6% and the capacity retention rate after 100 cycles is 91.3%, which is still far lower than the product of this invention.

[0069] The above application test results fully demonstrate that the ethylene tar-based liquid phase coated pitch prepared by this invention forms a uniform and dense carbon coating layer on the graphite anode surface, which can effectively reduce the side reactions between the electrolyte and graphite and inhibit the peeling of graphite sheets during charging and discharging. This significantly improves the first coulombic efficiency, reversible capacity, and especially the fast charging performance and cycle stability of lithium batteries, fully meeting the high requirements of new energy vehicles, energy storage equipment and other fields for the fast charging performance of lithium batteries.

[0070] The preparation process of this invention adopts a continuous operation mode, and the equipment used is all conventional industrial equipment in the fields of chemical and new energy materials, including a three-stage atmospheric distillation column, a liquid phase coating agent tank, a two-stage series high-pressure reactor, a cooler, a precision filter, a continuous mixer, a rotary kiln carbonization furnace, etc. No special customization is required, and the equipment selection and process parameters can be flexibly scaled up and adjusted according to the scale of industrial production. The distillation system can use an atmospheric distillation column with a diameter of 1-3m. The column height is designed according to the fraction separation requirements. It adopts a continuous feeding and discharging method to achieve large-scale fine fractionation of ethylene tar. The liquid phase coating agent tank can be 5-20m³ in volume and equipped with a variable frequency stirring device and an inert gas distributor to ensure the homogeneous mixing effect of large-scale materials. The catalytic crosslinking reaction system uses a 10-30m³ continuous high-pressure reactor, equipped with an automatic control system for temperature, pressure and gas flow to achieve precise and stable control of reaction conditions. In the negative electrode coating carbonization process, a continuous mixer and a rotary kiln carbonization furnace can be used to replace the tubular furnace in the laboratory to achieve large-scale coating modification of lithium battery negative electrode materials.

[0071] The technology of this invention has been verified through laboratory small-scale and pilot-scale tests. The product performance is stable, the process route is mature, and no harmful by-products are generated during the production process. The by-products such as fuel oil fractions can be recycled and reused, which meets industrial safety and environmental protection requirements. At the same time, this invention transforms ethylene tar, a low-value-added by-product of the ethylene industry, into a high-value lithium battery fast-charging anode coating material. The comprehensive utilization rate of ethylene tar is ≥98%, and the product yield is ≥56%, which reduces production costs and has good prospects for industrial scale-up applications. It can be widely used in the production of lithium battery anode materials in the fields of new energy vehicles, energy storage equipment, and portable electronic devices.

[0072] The same or similar labels correspond to the same or similar parts;

[0073] The terms used to describe positional relationships in the accompanying drawings are for illustrative purposes only and should not be construed as limiting this patent.

[0074] Obviously, the above embodiments of the present invention are merely examples for clearly illustrating the present invention, and are not intended to limit the implementation of the present invention. For those skilled in the art, other variations or modifications can be made based on the above description. It is neither necessary nor possible to exhaustively list all implementation methods here. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of the present invention should be included within the protection scope of the claims of the present invention.

Claims

1. A method for preparing ethylene tar-based liquid-phase coated pitch for use as a fast-charging negative electrode of lithium batteries, characterized in that, Includes the following steps: (1) Raw material distillation and fractionation: Ethylene tar is finely separated by a three-stage distillation system, and aromatic components are collected in two distillation ranges of 180-220℃ and 240-260℃, while the heavy reactive components are obtained at the same time; (2) Fraction homogenization and blending: The aromatic components at 180-220℃ and 240-260℃ obtained in step (1) are mixed at a mass ratio of 1:(0.5-2), and then the total mass of the resulting mixture is mixed with the reactive heavy components at a mass ratio of 1:(0.05-0.15). The mixture is homogenized under an inert gas atmosphere to obtain a liquid-phase coated asphalt precursor. (3) Catalytic crosslinking reaction: The liquid-coated asphalt precursor is subjected to a catalytic crosslinking reaction under a catalyst and an oxygen-containing atmosphere to obtain the ethylene tar-based liquid-coated asphalt.

2. The preparation method according to claim 1, characterized in that, The distillation process of the three-stage distillation system in step (1) is as follows: after the ethylene tar is preheated, it enters the first distillation column, and the fuel oil fraction is separated at the top of the column; the bottom material of the first column enters the second distillation column, and the light components are separated at the top of the column; part of the bottom material of the second column enters the third distillation column, and the third distillation column, by controlling the temperature at the top of the column, sequentially cuts and collects the aromatic components at 180-220℃, the aromatic components at 240-260℃, and the high-range fuel oil fraction, and the heavy reactive components are obtained at the bottom of the column.

3. The preparation method according to claim 1, characterized in that, The conditions for the homogenization reaction in step (2) are: reaction temperature 120-160℃, stirring speed 300-800r / min, and reaction time 1-4h.

4. The preparation method according to claim 1, characterized in that, The catalyst mentioned in step (3) is a metal oxide catalyst and / or a molecular sieve catalyst, and the amount of catalyst added is 0.1-1% of the total mass of the liquid-coated asphalt precursor.

5. The preparation method according to claim 1, characterized in that, The process conditions for the catalytic crosslinking reaction in step (3) are: reaction temperature 300-360℃, reaction pressure 0.5-1.5MPa, reaction time 2-8h; the oxygen-containing atmosphere is air with an oxygen volume fraction of 0-2% and an air flow rate of 1-3L / (min·kg) for liquid phase coated asphalt precursor.

6. The preparation method according to any one of claims 1-5, characterized in that, The ethylene tar in step (1) has an aromatic compound content of ≥80% and a total sulfur, nitrogen and ash content of ≤0.5%.

7. The preparation method according to any one of claims 1-5, characterized in that, The inert gas mentioned in step (2) is one or a mixture of nitrogen and argon.

8. An ethylene tar-based liquid-phase coated pitch for use as a fast-charging negative electrode of a lithium battery, characterized in that, The coated asphalt is prepared by any one of the preparation methods described in claims 1-7. The coated asphalt is liquid at room temperature, has a quinoline insoluble content of ≤0.1%, and a coking value of 18-28%.

9. The application of the ethylene tar-based liquid-phase coated pitch as described in claim 8 in lithium battery anode materials, characterized in that, The asphalt coating is applied to the surface of a graphite-based anode material, and then carbonized to obtain a fast-charging anode material for lithium batteries. The carbonization conditions are: carbonization temperature 900-1100℃, carbonization time 1-3h, and carbonization atmosphere is an inert gas atmosphere. The coating amount of the asphalt coating is 8-12% of the mass of the graphite-based anode material.

10. A lithium battery fast-charging negative electrode material, characterized in that, The anode material includes a graphite substrate and a carbon coating layer on the surface of the substrate. The carbon coating layer is formed by carbonization of the ethylene tar-based liquid phase coated pitch as described in claim 8. The anode material has a 2C / 0.5C capacity retention rate of ≥93%, an initial coulombic efficiency of ≥92%, and a capacity retention rate of ≥95% after 100 cycles.

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